KR101407160B1 - Insert and cutting tool - Google Patents

Abstract

The insert is made mainly of β-Si ₃ N ₄ and contains Mg and rare earth elements (Re) (Y, La, Ce, Er, Dy and Yb), Mg being 1.0 to 7.0 mol% And 0.4 to 1.0 mol% in terms of oxide, and the total amount thereof is 1.7 to 7.5 mol%. This insert is an inclined composition whose oxygen amount increases from the surface of the sintered body toward the inside and contains oxygen in an amount of 0.8 to 1.5 mass% from the surface to an inside of less than 0.5 mm, oxygen in an amount of 1.1 to 2.3 mass %, And the difference in oxygen amount is 0.1 to 1.0 mass%.

Description

[0001] INSERT AND CUTTING TOOL [0002]

The present invention relates to an insert and a cutting tool which are required to have abrasion resistance, and particularly to an insert and a cutting tool optimal for cutting a cast iron or the like.

A silicon nitride sintered body (silicon nitride sintered body) is conventionally used as a material for various cutting tools because it has excellent heat resistance and abrasion resistance.

However, since silicon nitride is ovoid-shaped, it is usually baked using a sintering auxiliary agent. When the amount of the silicon nitride is large, the performance of the sintered body is lowered.

Therefore, as in the following Patent Documents 1 to 5, the performance is improved from various viewpoints such as reduction of kinds and amount of preparation.

Patent Document 1 discloses a silicon nitride sintered body for cutting tools, which has extremely reduced abrasion resistance such as oxides of Mg, Zr and Ce, and particularly excellent wear resistance.

Patent Document 2 discloses a technique for improving abrasion resistance by reducing the amount of the internal preparation by volatilizing the preparation on the outermost surface of the sintered body.

Patent Document 3 discloses a technique for improving the wear resistance by increasing the surface hardness by forming? -Sialon on the surface of the silicon nitride-based sintered body by heat treatment.

Patent Document 4 discloses a technique of forming a hard phase having a Vickers hardness of 16 GPa or more at a depth of 10 탆 from the outermost surface of a sintered body by reducing the roughness of the sintered body by sintering in a SiO gas atmosphere.

Patent Document 5 discloses a technique of improving the thermal shock resistance by regulating the rare earth elements, Mg, Al, and the total amount, which are grain boundary forming components.

Patent Document 1: Japanese Patent No. 3550420

Patent Document 2: JP-A-2002-12474

Patent Document 3: JP-A-9-183667

Patent Document 4: JP-A-8-323509

Patent Document 5: Japanese Patent Application Laid-Open No. 11-268957

[Disclosure of the Invention]

[PROBLEMS TO BE SOLVED BY THE INVENTION]

However, in the technique described in Patent Document 1, there is a problem that the material is excellent in abrasion resistance, but is not sufficient in resistance to breakage because of a small amount of preparation, and is likely to be a material lacking in reliability.

In the technique described in Patent Document 2, although the composition of the sintering auxiliary agent is inclined, no consideration is given to SiO ₂ contained in the silicon nitride raw material which is the main component for forming the grain boundary phase together with the sintering auxiliary agent, so that sufficient abrasion resistance is obtained .

In the technique described in Patent Document 3, since α-sialon formed on the surface of the sintered body has lower strength than silicon nitride, there is a problem that the abrasion resistance is improved but the edge strength of the cutting insert is lowered.

In the technique described in Patent Document 4, since the abrasion resistance is not improved, there is a problem that the abrasion resistance of the cutting insert at high speed cutting is insufficient.

In the technique described in Patent Document 5, there is a problem that not only the abrasion resistance is lowered but also the thermal conductivity is lowered because the Al ₂ O ₃ content is large because the slope composition (graded composition) is not formed, and as a result, the resistance to breakage is lowered.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an insert and a cutting tool excellent in wear resistance and resistance to breakage.

[MEANS FOR SOLVING THE PROBLEMS]

The cutting edge temperature of the insert varies depending on the relative materials and cutting conditions, but it is generally said to be a high temperature of 800 ° C or higher. Therefore, it is important to have excellent heat resistance and chemical stability in order to improve abrasion resistance.

Since the grain boundary phase in the silicon nitride sintered body exists as an amorphous glass phase or a crystal phase composed of the auxiliary component and Si, N, and O, the heat resistance and the corrosion resistance are lower than that of silicon nitride. Therefore, the amount and composition of the grain boundary phase, .

In view of the above, firstly, it has been necessary to reduce the amount of grain boundary phase which is inferior in heat resistance, corrosion resistance and chemical stability.

The present inventors have found that the sintering assistant which can be densified even in a small amount and which acts as an auxiliary during silicon nitride firing and is easy to move and volatilize during sintering is selected so that the silicon nitride is slightly moved , It is possible to improve abrasion resistance, especially abrasive wear resistance in high-speed machining, by reducing the amount of oxygen from the inside to the surface by volatilization, and by optimizing the composition after volatilization, And an insert made of a silicon nitride sintered body that is compatible with each other can be obtained, thereby completing the present invention.

(1) The invention according to the first embodiment is characterized in that the main component is β-Si ₃ N ₄ and Mg contains rare earth elements Re (Y, La, Ce, Er, Dy and Yb) , And Re in an amount of 0.4 to 1.0 mol% in terms of oxide, and the total amount thereof is 1.7 to 7.5 mol%, wherein an inclination at which the oxygen amount increases from the surface of the sintered body toward the inside (Inclined composition) containing 0.8 to 1.5% by mass of oxygen and 1.1 to 2.3% by mass of oxygen within 0.5 mm or more from the surface to an inside of less than 0.5 mm from the surface, By mass to 1.0% by mass.

First, Mg and rare earth elements (Re) (Y, La, Ce, Er, Dy and Yb) are contained in an amount of less than 1.0 mol% in terms of MgO, less than 0.4 mol% , Sufficient sinterability can not be obtained. If the upper limit is exceeded, the auxiliary components remain in the sintered body unnecessarily, which is not preferable.

Among them, Mg is not only effective for sintering by lowering the melting point and viscosity of the intergranular phase together with SiO ₂ , but also Mg and SiO ₂ are easily set and evaporated to the surface portion, so that it is indispensable to obtain a desired insert It is an element.

On the other hand, the rare earth element Re (Y, La, Ce, Er, Dy, Yb) not only works effectively to needle-form silicon nitride particles but also has a small ionic radius, And it is also easy to move and evaporate to the surface portion, which is optimal for obtaining the desired insert.

Therefore, in the present invention, the composition of Mg and the rare earth element Re (Y, La, Ce, Er, Dy, Yb) is defined as described above.

When the amount of oxygen in the sintered body surface is less than 0.5 mm (less than 0.8 mass%), the so-called white portion which is not densified remains, while when it exceeds 1.5 mass%, sufficient abrasion resistance is not obtained.

When the amount of oxygen within 0.5 mm or more from the surface of the sintered body is less than 1.0% by mass, the needle-like structure peculiar to silicon nitride does not grow and sufficient resistance to cracking can not be obtained. When oxygen content exceeds 2.3% by mass, heat resistance deteriorates, The abrasion resistance is lowered.

If the difference between the oxygen content from the surface to 0.5 mm and the oxygen content within 0.5 mm or more is less than 0.1 mass%, it is difficult to achieve both abrasion resistance and crack resistance because the inclination is too gentle. When the difference is more than 1.0 mass% The residual stress is generated due to the difference between the surface tension and the tensile stress, and the surface is liable to be peeled off.

Therefore, in the present invention, the oxygen amount is defined as described above.

Therefore, in the insert of the present invention, excellent wear resistance and breakage resistance can be exhibited by the above-described structure, and therefore it is possible to cut, for example, cast iron or the like at a high speed.

(2) According to the invention as a second embodiment, the rare earth element (Re) is Yb, Mg is 1.0~5.5mol% in terms of MgO, Yb is contained in the 0.4~1.0mol% Yb ₂ O ₃ equivalent, respectively, and And the total amount is 1.7 to 6.0 mol%.

The combination of Yb, that is, Mg and Yb, as rare earth element (Re), is an optimum combination for both abrasion resistance and resistance to breakage because it is effective in sintering in small amounts and is easy to volatilize on the surface. Therefore, in the present invention, the composition of Mg and Yb is defined as described above.

(3) In the invention of the third embodiment, the thermal conductivity at room temperature is 45 W / m · K or more at the outer side (surface side) than at the depth of 1.0 mm from the surface, 40 W / Or more. Here, 'room temperature' is 25 ° C (hereinafter the same).

With respect to the thermal conductivity, a high-temperature side is easy to dissipate heat, and the heat of the insert can be relaxed, which is effective in mitigating thermal shock.

In the present invention, since the thermal conductivity at room temperature is 45 W / m · K or more at the outer side (surface side) than the depth of 1.0 mm from the surface and is 40 W / m · K or more at 1.0 mm or more from the surface, The defect of the silicon nitride sintered body (and thus the insert) due to growth can be remarkably suppressed.

(4) The invention of the fourth embodiment is characterized in that the tensile strength at room temperature (three point bending strength: JIS R1601) is 900 MPa or more.

The insert of the present invention has an elastic strength at room temperature (three point bending strength: JIS R1601) of 900 MPa or more, preferably 1,000 MPa or more.

In the case of cutting using the insert of the present invention, the larger the strength of the sintered body constituting the insert is, the more excellent not only the strength but also the thermal shock resistance, the stable machining becomes possible. Therefore, the insert having the three-point bending strength is particularly optimum. That is, stable machining becomes possible by using the insert of the present invention having a room temperature strength of 900 MPa or more.

In the insert of the present invention, when the total amount of ZrO ₂ and Al ₂ O ₃ , which are auxiliary components, is 0.6% by mass or less, the thermal conductivity is maintained at 45 W / m · K or more so that the performance is not deteriorated and the sinterability can be improved Do. When the total content of ZrO ₂ and Al ₂ O _{3 as} the auxiliary ingredients is more than 0.6% by mass, the movement of the auxiliary component to the surface is dull and not sufficiently inclined, so that the abrasion resistance is lowered and the thermal conductivity is lowered. And the resistance to defects is lowered.

(5) The invention of the fifth embodiment is characterized in that the grain boundary phase contains crystals composed of Yb element, Mg element, Si element, O element and N element.

By precipitating crystals composed of Yb element, Mg element, Si element, O element and N element on the grain boundary of the insert consisting of the silicon nitride sintered body, it is possible to reduce the glass phase present in the first grain boundary phase even at a small addition amount, It is possible to provide an insert having excellent wear resistance and breakage resistance. The crystal composed of the Yb element, the Mg element, the Si element, the O element and the N element is not particularly limited. However, in the presence of the grain boundary phase, the abrasion resistance and the breakage resistance of the silicon nitride sintered body can be particularly improved. YbMgSi ₂ O ₅ < / RTI >

The insert made of the silicon nitride sintered body according to the present invention is composed of a main crystal phase mainly composed of silicon nitride (hereinafter sometimes referred to as "Si ₃ N ₄ ") and one or more kinds of sialon crystal grains, a Yb element, (The compound giving the crystal is sometimes referred to as "YbMgSi compound" hereinafter)) composed of an element, an O element and an N element.

The main crystalline phase contains at least one crystal grain of silicon nitride and / or sialon. The silicon nitride contained in the main crystal phase contains β-Si ₃ N ₄ as a main component and may be β-Si ₃ N ₄ alone or a mixture of α-Si ₃ N ₄ and β-Si ₃ N ₄ . That the silicon nitride is a ratio, i.e. ratio of α-Si ₃ N ₄ and the α β-Si ₃ N _4, when a mixture of the α-Si ₃ N ₄ is 0 - 30% being preferred. If the? ratio exceeds 30%, there may be a problem that the mechanical properties such as toughness are lowered due to reduction of the needle-like particles in the sintered body. α rate of expression from the α-Si ₃ N ₄ of the peak intensity (Iα) and peak intensity (Iβ) of β-Si ₃ N ₄ as determined by X-ray diffraction method: [Iα / (Iα + Iβ )] × 100 As shown in FIG.

The content of oxygen as an impurity contained in silicon nitride is usually 0.8 to 2% by mass. If the oxygen content is low, the sinterability is deteriorated. If the oxygen content is large, the heat resistance may be lowered or the thermal conductivity may be lowered. The optimum average particle diameter of the silicon nitride is 0.5 to 1.6 탆. If the average particle diameter is less than 0.5 [micro] m, the moldability may be deteriorated.

The sialon contained in the main crystal phase is a generic name of a compound of Si-Al-ON system. α- sialon is α-Si ₃ N ₄ crystal and the silicon and aluminum, and oxygen is located in the metal ion partially substituted employed (固溶) as soon at the same time the charge compensation of the nitrogen intrusion compound employed in the, between the β- Alon is a compound in which aluminum and oxygen are partially substituted and solved at positions of silicon and nitrogen in the crystal of? -Si ₃ N ₄ .

The sialon contained in the main crystal phase may be any of α-sialon, β-sialon, α-sialon and β-sialon, though not particularly limited. When sialon is a mixture of? -Sialon and? -Sialon, the ratio of? -Sialon, that is, the? Ratio is preferably 30% or less. When the? ratio exceeds 30%, mechanical properties such as toughness deterioration are lowered due to reduction of needle-shaped particles in the sintered body, and as a result, the sintered body of silicon nitride is likely to have poor resistance to scratching. The? ratio can be calculated in the same manner as the? ratio of Si ₃ N ₄ from the peak intensity of? -sialon and the peak intensity of? -sialon determined by X-ray diffractometry.

The main crystal phase may contain at least one kind of crystal grains of silicon nitride and sialon. The main crystal phase may contain crystal grains of silicon nitride mainly or may contain mainly sialon crystal grains. The crystal grains of silicon nitride And sialon crystal grains may be mainly contained.

The insert comprising the silicon nitride sintered body according to the present invention is characterized in that it comprises at least one of the above-mentioned crystal grains of silicon nitride and / or sialon, a YbMgSi compound contained in the grain boundary phase to be described later and a crystal phase and / In the range of 85 to 98 mass%, preferably 90 to 97 mass%, of the main crystal phase, that is, one or more kinds of crystal grains of silicon nitride and / or sialon so that the total amount of the compounds is 100 mass% do. If the content of the main crystal phase exceeds 98% by mass, the abrasion resistance may deteriorate due to the reduced sinterability. If the content is less than 85% by mass, the excellent mechanical properties and heat resistance of silicon nitride or sialon itself There is something that can not be done.

(6) In the invention of the sixth embodiment, in the X-ray diffraction chart of the insert of the silicon nitride sintered body, the peak intensity (I _Yb ) showing the maximum intensity in the peak based on YbMgSi ₂ O ₅ N in the crystal is And is not less than 0% and not more than 10% with respect to the peak intensity (I _S ) indicating the maximum intensity in the peak based on silicon nitride.

The peak intensity (I _Yb ) showing the maximum intensity in the peak based on YbMgSi ₂ O ₅ N is contained so as to be 1 to 9% with respect to the peak intensity (I _S ) showing the maximum intensity in the peak based on silicon nitride or sialon , More preferably from 1.5 to 3.0%, and particularly preferably from 1.5 to 3.0%. When the content of the YbMgSi compound in the silicon nitride is within the above range, the insert made of a silicon nitride sintered body exhibits particularly excellent wear resistance and breakage resistance, and exhibits particularly excellent wear resistance even in high speed cutting at a high temperature of 800 DEG C or higher. In addition, the peak intensity (I _Yb ) and the peak intensity (I _S ) are determined as the height from the baseline in the X-ray diffraction chart of the silicon nitride sintered body.

The YbMgSi compound is usually contained in the grain boundary phase, but a part thereof may be contained in the main crystal phase.

The grain boundary phase may have a crystal phase and / or a glass phase mainly composed of elements constituting a sintering assistant etc. in addition to the YbMgSi compound. The crystalline phase and / or the glass phase are liquefied at the time of sintering, contributing to sintering, and then solidified at the time of cooling to form a glass phase or a crystal phase, such as a sintering aid, a silicon component contained as silicon nitride and silicon nitride as impurities. Examples of such a crystal phase include a YAG phase, a YAM phase, and Yb ₂ Si ₂ O _{7. Since} such a crystal phase is generally low in toughness, it is controlled to a suitable amount (mass%).

In addition, since the glass phase generally has a low melting point, a low hardness and a low hardness, it is controlled to an appropriate amount (mass%) in consideration of sintering property when the sintered body is sintered. The abundance of these crystal phases and glass phases is suitably adjusted by the silicon nitride sintered body and the YbMgSi compound, but it is preferable that the crystal phase and the glass phase are extremely small and substantially not exist.

(7) The invention of the seventh embodiment is a cutting tool equipped with an insert according to any one of the first to sixth embodiments described above on a holder.

It is possible to optimally perform the cutting work by using the cutting tool having the insert mounted on the holder.

Here, when the silicon nitride sintered body (i.e., insert) described above is produced, it is optimal to use the MgCO ₃ raw material powder as the Mg source.

In other words, MgO powder is generally used as a raw material of the silicon nitride sintered body. However, in the silicon nitride sintered body obtained by volatilizing the auxiliary component on the surface as in the present invention, a so-called white part in which the surface is excessively volatilized do.

Therefore, when MgCO ₃ is used as a starting material, the presence of CO ₂ (MgCO ₃ ? MgO + CO _2? ) Generated by decomposition at relatively low temperature during firing is suppressed in the nitrogen atmosphere, Therefore, a silicon nitride sintered body having a stable surface which is not whitened can be produced.

1 (a) is a perspective view of an insert of the embodiment, and (b) is a perspective view enlarging and showing a nose portion of the insert. Fig.

2 is an explanatory view showing a cutting method.

3 is an explanatory diagram showing Table 1 showing firing conditions and compositional composition of the sample in the experimental example.

4 is an explanatory view showing Table 2 showing the experimental results.

5 is an X-ray diffraction chart of the sample 2 in the example.

6, (a) is a cross-sectional view of the workpiece, (b) is a longitudinal sectional view of the workpiece, and (c) is an explanatory diagram showing the cutting direction.

7 is a graph showing experimental results.

[Description of Symbols]

1 - insert 3 - cutting edge

5 - chamfer 7 - nose

9 - Holder 11 - Cutting tool

BEST MODE FOR CARRYING OUT THE INVENTION [

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment Mode]

a) First, the structure of the insert of the present embodiment will be described.

As shown in Figs. 1 (a) and 1 (b), the insert 1 of the present embodiment is a cutting tip of a substantially square plate shape (i.e., an ISO standard SNGN120408 shape) made of a silicon nitride sintered body.

The insert 1 has a cutting edge 3 at a corner of its both surfaces (inclined surfaces), and a chamfer 5 is formed on the cutting edge 3. In addition, the nose 7 of the insert 1 is smoothly curved.

The insert 1 of the present embodiment contains Mg and rare earth elements Re (Y, La, Ce, Er, Dy, Yb), Mg is 1.0 to 7.0 mol% in terms of MgO, Re is 0.4 To 1.0 mol%, respectively, and the total amount thereof is 1.7 to 7.5 mol%.

The insert 1 has an inclined composition (graded composition) in which the amount of oxygen increases from the surface of the sintered body toward the inside, and oxygen is contained in an amount of 0.8 to 1.5 mass% and 0.5 Mm or more, oxygen is contained in 1.1 to 2.3 mass%, and the difference in oxygen amount is 0.1 to 1.0 mass%.

The insert 1 has a thermal conductivity of at least 45 W / m 占 에서 at room temperature and a tensile strength of not less than 40 W / m 占 내부 in 1.0 mm or more from the surface and a tensile strength at the same room temperature (3 point bending strength: JIS R1601) is 900 MPa or more.

The insert 1 is made of a silicon nitride sintered body containing crystals composed of Yb element, Mg element, Si element, O element and N element in the grain boundary phase.

This insert (1) is characterized in that, in the X-ray diffraction chart, the peak intensity (I _Yb ) indicating the maximum intensity among the peaks based on YbMgSi ₂ O ₅ N in the crystal is a peak based on silicon nitride or sialon Is not less than 0% and not more than 10% with respect to the peak intensity (I _S ) indicating the maximum intensity.

Accordingly, the insert 1 of this embodiment has both high abrasion resistance and breakage resistance as shown in the experimental example described later by this structure.

The above-mentioned insert 1 is used as a cutting tool 11, for example, joined to the tip end of a forcible columnar holder 9, as shown in Fig.

For example, when cutting is performed using the insert 1, the nose 7 between the front flank and the side flank is pressed against the rotating workpiece W to perform cutting.

b) Next, a method of manufacturing the insert of the present embodiment will be described.

First, α-Si ₃ N ₄ powder having an average particle diameter of 1.0 μm or less as a main component and Yb ₂ O ₃ powder, Y ₂ O ₃ powder, La ₂ O ₃ powder, CeO ₂ powder, Er ₂ O ₃ powder, Dy ₂ O ₃ powder, MgO powder, MgCO ₃ powder, Al ₂ O ₃ powder and ZrO ₂ powder were weighed in the mixing ratios shown in FIG. 3 (Table 1).

The weighed material was mixed for 96 hours in an ethanol or water solvent using an inner wall port made of silicon nitride and a ball made of silicon nitride so as to minimize the incorporation of Al ₂ O ₃ to obtain a slurry.

The slurry was passed through a sieve of 325 mesh, added with 5.0 wt% of a wax-based organic binder dissolved in ethanol or water, and spray-dried.

Then, the obtained granulated powder was press-molded into the shape of SNGN120408 of ISO standard, and then degreased at 600 deg. C for 60 minutes in a nitrogen atmosphere at 1 atm in a heating apparatus.

Subsequently, the degreased molded body was first sintered. Specifically, in a SiC crucible or a silicon nitride crucible, the crucible is held at 1800 to 1900 ° C in the first step and at 60 to 180 minutes in the atmospheric pressure (atmospheric pressure of the samples 1 to 20) shown in FIG. 3 (table 1) In the second step, sintering was carried out by holding at a temperature lower than the first step (1800 DEG C or lower) and an atmospheric pressure or lower than the atmospheric pressure for 120 to 360 minutes.

The thus-obtained silicon nitride sintered body was polished into the shape of SNGN120408 of ISO standard to obtain insert (1) of this embodiment, that is, inserts (samples 1 to 20) of the embodiment within the scope of the present invention used in the experiment described later.

As described above, in the present embodiment, the raw material (particularly, MgCO ₃ ) of the above-described compounding composition is used to perform the first calcination at a low pressure of 2 atm or less. Thus, the insert 1 having the above- .

In addition, the inserts (samples A to O) of the comparative example outside the scope of the present invention were also produced by the above-mentioned method (the conditions shown in Fig. 3 (Table 1) were adopted).

[Experimental Example]

Next, an experimental example using each sample will be described.

a) First, the measurement method of the characteristics of the insert of each sample will be described.

◎ The amount of each element (excluding nonmetal elements) in each sample (sintered body) is analyzed by well-known fluorescent X-ray or chemical analysis, and each element is regarded as a compound such as oxide or nitride, For Si, Si ₃ N ₄ , Mg for MgO, Yb for Yb ₂ O ₃ , and the like, mass ratios were calculated.

The prepared component in the sintered body in FIG. 4 (Table 2) to be described later is in mol%, but it can be converted to the mass% by multiplying the number by the molecular weight of each component and adjusting the whole sintered body to be 100% .

◎ The amount of oxygen was measured by cutting each specimen at 0.5 mm from its surface as a boundary, and then pulverizing the specimen divided into the front side and the inside side from the boundary by impulse heating and melting and measuring the oxygen amount by non-dispersion infrared absorption method Respectively.

? The thermal conductivity was evaluated by grinding each specimen in the shape of a disk having a diameter of 10 mm and a thickness of 1 to 2 mm and measuring the value at room temperature by the JIS R1611 method (commonly referred to as "laser flash method"). Specifically, the thermal conductivity from the surface to 1 mm was measured with a sample having a thickness of 1 mm, and with respect to the thermal conductivity within 1 mm from the surface, the sample was measured with a sample having a thickness of 2 mm.

◎ For the strength, a sample having a length of 3 mm × 4 mm × 36 mm or more was prepared for each sample, and the sample was polished and subjected to a three-point bending test at room temperature by JIS R1601 at least five times. Respectively. Further, the span at the time of the test is preferably 30 mm, but it may be smaller (lower limit 10 mm).

◎ α-Si ₃ N ₄ is β-Si ₃ N whether or ₄ is in and Yb element, Mg elements, in order to examine the crystal made of a Si atom, an O element and an N element is whether or not the grain boundary phase, the respective samples Using an X-ray diffractometer manufactured by Riken Electric Industry Co., Ltd., X-ray diffraction of 2? In the range of 20 to 70 was performed under the condition of a Cu tube, a gonearmeter in a vertical direction, and a tube voltage of 50 kV. The peak in the obtained X-ray diffraction chart was estimated with reference to PDF card data. In the X-ray diffraction chart of each sample, a peak of? -Si ₃ N ₄ was recognized, and? -Si ₃ N ₄ used as a raw material was confirmed to be? -Si ₃ N ₄ .

In the X-ray diffraction charts of Samples 1, 2, 4, and 13 to 18, a distinctive peak for YbMgSi ₂ O ₅ N was recognized in addition to the specific peak for β-Si ₃ N ₄ (YbMgSi ₂ O ₅ N PDF card 48-1634). In the X-ray diffraction chart of sample N, a specific peak for Yb ₂ Si ₂ O ₇ was recognized in addition to a specific peak for β-Si ₃ N ₄ . On the other hand, in the X-ray diffraction charts of Samples 3, 5 to 12, 19 and 20 and Samples A to M and O, no peak distinctive to the crystals of the YbMgSi compound was found other than the peculiar peak for β-Si ₃ N ₄ .

The peak intensity of the X-ray diffraction chart ratio, in the diffraction chart of each X-ray, YbMgSi ₂ O ₅ N peak intensity (I _Yb) indicating a maximum intensity of the characteristic peaks for the β-Si ₃ N ₄ or sialon to obtain respectively the peak intensity (I _S) that represents the maximum intensity of the peak on the basis of the height from the respective X-ray base line of the diffraction chart, formula (I _Yb / I _S) calculated according to × 100 (%) based on Respectively. For example, an X-ray diffraction chart of the sample 2 in Fig. 4 (Table 2) is shown in Fig.

In this X-ray diffraction chart, the peak showing the maximum intensity among the specific peaks (indicated by a black circle in FIG. 5) for YbMgSi ₂ O ₅ N is recognized in the vicinity of 2 ° (deg) at 30 ° It referred to} the intensity _{'I Yb', β-Si} 3 N 4 peak based on the peak indicating the maximum intensity of the (in Fig. 5 peaks marked with ●) is therefore recognized in the vicinity of 2θ (deg) is 36 ° (This peak intensity is referred to as 'I _S '), and the peak intensity (I _Yb ) and the peak intensity (I _S ) were used. The peak intensity ratio of each insert thus calculated is shown in Fig. 4 (Table 2).

Each sample was measured for density by the Archimedes method and divided by the theoretical density to calculate the theoretical density ratio. All the samples of the scope of the present invention (Examples) were sufficiently densified because the theoretical density ratio was sufficiently high (more specifically, not less than 99.0) and no micropores remained in the sintered body.

Measurement results other than the theoretical density ratio are shown in Fig. 4 (Table 2).

b) Next, the performance test of the insert of each sample will be described.

(1) abrasive wear resistance

As shown in Fig. 6, an insert having a shape of SNGN120408 of 0.2 mm and a chamfer of 0.2 mm is used to select an FC 200 in which a scan (sand) is left on both end faces as a workpiece, and the insert is moved in the direction of arrow A to perform cutting Respectively.

Specifically, the cutting speed; 500 mm / min, cutting depth; 1.5 mm, feed rate; The cutting operation was performed under the condition of 0.2 mm / rotation and dry, and the flank maximum wear amount was measured and the abrasion wear amount (unit: mm) was determined.

In Fig. 6, L1 is 260 mm, L2 is 300 mm, L3 is 100 mm, and the wall thickness is 20 mm.

The results are shown in Fig. 4 (Table 2).

(2) Internal defectiveness

SNGN432 shape, insert with a chamfer 0.1 mm.

Specifically, FC200 was selected as the workpiece, and cutting speed; 150 m / min, cutting depth; 2.0 mm, and the feed rate is 0.60 mm / rev, and is incremented by 0.05 mm / rotation for each process path. The cutting process is performed under the dry condition, and evaluation is made by the feed rate to the defect Respectively.

The results are shown in Fig. 7 and Fig. 4 (Table 2).

As is apparent from Fig. 7 and Fig. 4 (Table 2), the samples of the examples of the present invention have a lower abrasion wear amount and a higher feed rate at the time of defect than the samples of the comparative example, .

It is needless to say that the present invention is not limited to the above-described embodiments and examples, but can be carried out in various forms within the scope not departing from the present invention.

Claims (7)

as a main component a β-Si ₃ N _4, and but containing Mg and a rare earth element (Re) (Y, La, Ce, Er, Dy, Yb), Mg is 1.0~7.0mol% in terms of MgO, Re is in terms of oxide By mass of silicon nitride, and 0.4 to 1.0% by mole of silicon nitride, and the total amount is 1.7 to 7.5% by mole, An inclined composition in which the amount of oxygen increases from the surface of the sintered body toward the inside and contains oxygen in an amount of 0.8 to 1.5% by mass, oxygen in an amount of 0.5 mm or more from the surface and 1.1 to 2.3% , And the difference in oxygen amount is 0.1 to 1.0 mass%. The method according to claim 1, A rare earth element (Re) is Yb, Mg contains at 1.0~5.5mol%, Yb is 0.4~1.0mol% Yb ₂ O ₃ in terms of the terms of MgO, respectively, characterized in that the sum of the% 1.7~6.0mol Insert. The method according to claim 1, Wherein the thermal conductivity at room temperature is 45 W / m · K or more at the outer side than the depth of 1.0 mm from the surface, and 40 W / m · K or more at the inner side of 1.0 mm or more from the surface. The method according to claim 1, Wherein the tensile strength at room temperature (three-point bending strength: JIS R1601) is 900 MPa or more. The method according to claim 1, Wherein the grain boundary phase contains crystals composed of Yb element, Mg element, Si element, O element and N element in the grain boundary phase. The method of claim 5, In the X-ray diffraction chart of the insert of the silicon nitride sintered body, the peak intensity (I _Yb ) showing the maximum intensity in the peak based on YbMgSi ₂ O ₅ N in the crystal is a peak showing the maximum intensity among the peaks based on silicon nitride Is not less than 0% and not more than 10% with respect to the strength (I _S ). A cutting tool characterized in that the insert according to any one of claims 1 to 6 is mounted on a holder.

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